Discharge of rinse waters associated with dyeing processes results in the discoloration of large volumes of water from which the pigment or colored matter cannot be easily removed. The American textile industry alone consumes several million pounds of dye each year, and a substantial portion thereof finds its way into various waste streams. Current treatment methods for these waste streams may be classed as biological or physical-chemical in nature.
Bacterial degradation and coagulation of dye wastes occurs in sanitary sewage treatment, but here, acceptability of the dye waste is dependent upon the percentage of dye that can be removed in the treatment. In many cases dye wastes are just too resistant to undergo microbial degradation in the time required for conventional waste treatment, and in some cases the resultant treatment products may be more toxic than the original material. As a result, biological processes may be unable to provide sufficient treatment for dye wastes to produce a product that is free of visible tint and toxic residuals.
Several physical or chemical methods for the treatment of dye wastes are known, but these systems seem to suffer from either low practical efficiency or associated high costs. Common treatments in this realm consist of trying to absorb the colored matter on freshly precipitated metal hydroxides, or coagulated polymeric materials, or on clay particles. The color removal in these systems is not complete and is dependent upon the total amount of coagulant or adsorbent material added in the treatment. The greater the addition of coagulant or adsorbent, the better the color removal; however, large additions of these materials results in the production of copious amounts of colored sludge that may contain only a few percent dry solids; and thereby, creates sludge disposal problems. Waste dye preparations and rinse waters may also be purified by adsorption of the colored matter on activated carbon. This method has been found to be effective, but the high costs associated with the activated carbon adsorption process most often renders it an unfeasible option. Some efforts have also been made to degrade dyestuffs by electrochemical means; however, the power consumption necessary for color removal also makes this an expensive solution to the dye waste problem.
In processes for the dyeing of textile articles, such as fibers, cloths and yarns etc., the dyed article is customarily subjected to a subsequent treatment with an inorganic salt solution to set the dye in the pores of the article thereby rendering color fastness to the article. For this purpose the dyed article is first rinsed with water and subsequently treated with a salt solution of a concentration from 30 to about 80 g/liter. After use both the rinse water and the salt solution, which now is colored as a result of the treatment, are discharged to the environment. In many instances this discharge poses a serious problem for the processor especially when the soluble solids concentration of the effluents from the overall process approaches the maximum tolerable limit in accordance with local prevailing pollution control standards.
It is therefore an object of the present invention to provide a process for the waste removal of colorants from effluent streams.
It is another object of the invention to provide a process for the pollution-free removal of excess colorants from dyed articles which process is integrated with the dyeing process and can result in increased color fastness of the dyed article.
Other objects of the invention will become apparent from the disclosure and appended claims.